Combating the impact of contamination in solar cell production
Combating the impact of
contamination in solar cell
production
by Sheila Hamilton, Teknek, Renfrew, Renfrewshire, UK
How contamination addition, the connec-
Photo voltaic cell manufactur- affects PV module
“Conductive materials
tor circuits face similar
ers today are under increasing
production depends
(debris) can result
problems to first
pressure to increase yields and
on which of the generation PV cells in
improve the efficiency of their
three types of solar
in corrosion of the
terms of tombstoning,
products. This has become
cell being produced.
finished product and
blow-outs and short
more imperative as the cost
In first generation circuits, if contamina-
solar cells—silicon may only show up in
of raw materials has risen
tion is present. Like-
wafers—the presence wise, at the encapsula-
dramatically in recent years.
the field later in the
of dirt and debris tion stage, the glass or
One of the main barriers to
can affect the screen product’s life.” film must be cleaned
achieving this is the inci-
printing process, if maximum efficiency
dence of contamination in leading to problems is to be achieved.
the production environment. such as tombstoning, Third generation
If contamination is present
pin holes, open and short circuits. Contami- solar cells use screen printing techniques
before coating, metallization,
nation of solder joints can lead to miniature similar to those employed in the microelec-
printing or lamination yields
‘blow outs’ as organic materials vaporize and tronics sector. This type of cell generally has
may be affected.
expand, rapidly causing voids and dry joints. a lower efficiency than generations one and
This article will look at
The solar cell modules are then encap- two, so it is important that contamination
the impact of contamination,
sulated in an EVA film. If dust or particles does not lower the efficiency even more.
become trapped between the film and solar The substrate and stencil must therefore
the key sources of contamina-
cells, it can affect the efficiency of the cells be thoroughly cleaned before each printing
tion and the problems which
by blocking sunlight. Given that efficiencies stage. As the collector patterns become ever
can arise, and suggests pos-
are already generally low, this is something finer to produce greater efficiencies, the
sible solutions to negate the manufacturers will wish to avoid. Even impact of particles becomes greater. The sub-
effects of contamination. particles too small to be seen, due to a tent- strate used for printing is generally polyester
ing effect, can produce visible defects in the film or thin sheet steel. These substrates ar-
laminated surface (fish eyes). rive for coating or deposition direct from the
The second generation of PV cells—vac- supplier and are frequently contaminated
Keywords: Contact Cleaning,
uum metalised—are more efficient; however with debris from the manufacturing process.
Printing, Contamination,
the substrate needs to be cleaned before and For example, rolls of polyester are usually slit
Debris, Yield
during the deposition chamber process. In to a specific width and slitter dust can
PV Technology
cSi Thin Film Technologies
Copper Indium Cadmium Tellurid Silicon Based Flexible Substrates
Copper Indium aSi Silicon Based
Gallium Diselenid
Copper Indium Sulfite aSi/µcSi CIS/CIGS
Figure 1. PV tcchnologies.
8 – Global Solar Technology – November/December 2008 www.globalsolartechnology.com
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